This application for a Tobacco Center of Regulatory Science (TCORS) from the University of Southern California (USC) addresses the cross-ciutting theme of tobacco use among diverse populations, proposing an agenda of methods development and research that will assure that the activities of the Food and Drug Administration's (FDA) Center for Tobacco Products (CTP) reach many groups at risk for nicotine addiction and the adverse consequences of tobacco use. The proposed USC TCORS directly responds to RFA-DA-13- 003 with a highly experienced multi-disciplinary team of investigators who already work together on tobacco research in diverse populations considered vulnerable to tobacco use and addiction. These populations are distinguished by high and/or expanding tobacco use rates relative to other US populations, and may also be particularly vulnerable to tobacco use influences through tobacco industry marketing, social media communications, and cultural networks that present a tobacco use norm. There are three overall research aims of this TCORS: 1) evaluate marketing, social influence, social media, and network influences on tobacco use and product choice, emphasizing vulnerable populations, with the ultimate aim of identifying ways to reverse or counteract these influences; 2) examine tobacco product distribution and regulation among local vendors, whose stores are a key point for purchase, contact with industry marketing and promotion, and potentially for education about actions of the FDA and product risks; 3) examine different topographies of tobacco use, integrating phenotypic variables with cultural and environmental variables to determine how future tobacco control initiatives may be tailored to different vulnerable groups. Meeting the research aims, along with the training activities, will provide evidence that will enhance FDA's impact as it seeks to advance public health using strategies based in regulation and education. The research acknowledges the dynamic interplay between FDA actions and industry responses and explores these dynamics across vulnerable populations.